Princess Charlotte, three, left her brother Prince George, four, in stitches as she was seen squishing her nose against the window before making a series of hilarious faces towards the crowds.

Prince George is seen laughing at his sister Charlotte as she pulls funny faces [Joe Dias/NEWSPIX INTERNATIONAL]

Prince George and Princess Charlotte were spotted at a window of Buckingham Palace [Wenn]

Looking adorable in a blue floral dress, little Charlotte screamed and cheered from behind the glass, as George laughed at his younger sister.

The royal appearance at Buckingham Palace came after a service at Westminster Abbey earlier in the day.

Just one day after attending the christening of Prince Louis, Kate Middleton and Prince William, Prince Harry and Meghan Markle were pictured arriving for a service to mark the centenary of the Royal Air Force at Westminster Abbey in central London.

Prince William, Duke of Cambridge, Meghan, Duchess of Sussex and Prince Harry, Duke of Sussex attending an event to mark the centenary of the RAF [Getty]